Automated optical link power control

Abstract

A system, apparatus and method are described for controlling the gain across one or more amplifier nodes within an optical span. In one embodiment, a fast local amplifier constant gain control loop is provided that maintains a constant gain across an amplifier node for each of the channels within an optical signal. A slow link level gain setting control loop is provided to set and/or adjust the target gain on the amplifier node(s). A gain adjust sequence is performed by the slow link level gain setting control loop to adjust the target gain(s) in response to various events and mechanisms. A “time of flight” protection method is also provided to ensure consistency between the fast local amplifier gain control loop and the slow link level gain setting control loop.

1. A system for controlling optical link power, the system comprising:
 a head node that transmits an optical signal, having a plurality of optical channels, on an optical link; 
 a plurality of amplifier nodes, serially coupled to the head node; 
 an end node, coupled to the plurality of amplifier nodes, that receives the optical signal from the optical link; 
 an amplifier gain control loop, coupled across one of the plurality of amplifier nodes, the amplifier gain control loop controlling said one of the plurality of amplifier nodes such that said one of the plurality of amplifier nodes applies a constant gain to each of the plurality of optical channels; and 
 a link gain setting control loop coupled between the head end node and said one of the plurality of amplifier nodes, the link gain setting control loop adjusting a target gain value for said one of the plurality of amplifier nodes. 
 
   
   
     2. The system of  claim 1  wherein, the optical signal is a first optical signal, and information is communicated to the link gain setting control loop via a second optical signal propagating on the optical link. 
   
   
     3. The system of  claim 1  wherein the adjustment to the target gain value is performed by the link gain setting control loop in response to a gain adjust request received by the head end node from the first one of the plurality of amplifier nodes. 
   
   
     4. The system of  claim 1  wherein the link gain setting control loop adjusts the target gain value in response to a change in a number of the plurality of optical channels. 
   
   
     5. The system of  claim 1 , wherein the amplifier gain control loop is a first amplifier gain control loop, the link gain setting control loop is a first link gain setting control loop, the constant gain is a first constant gain, the target gain is a first target gain value, and said one of the plurality of amplifier nodes is a first one of the plurality of amplifier nodes, the system further comprising:
 a second amplifier gain control loop coupled across a second one of the plurality of amplifier nodes, the second amplifier gain control loop controlling said second one of the plurality of amplifier nodes such that said second one of the plurality of amplifier nodes applies a second constant gain to each of the plurality of optical channels; and 
 a second link gain setting control loop, coupled between the head end node and the second one of the plurality of amplifier nodes, that adjusts a second target gain value for the second one of the plurality of amplifier nodes. 
 
   
   
     6. The system of  claim 5  wherein a second gain adjustment process on the second one of the plurality of amplifier nodes is only performed if a first gain adjustment process on the first one of the plurality of amplifier nodes was successfully completed. 
   
   
     7. The system of  claim 1  wherein time of flight protection is provided to detect a parameter change at the head end node or the first one of the plurality of amplifier nodes. 
   
   
     8. A system comprising:
 a head node that transmits an optical signal, having a plurality of optical channels, on an optical link; 
 a plurality of amplifier nodes, serially coupled to the head node, that operate in a constant power mode; 
 an end node, coupled to the plurality of amplifier nodes, that receives the optical signal from the optical link; 
 an amplifier gain control loop, coupled across an amplifier node within the plurality of amplifier nodes, that provides constant output power across each of the plurality of optical channels; and 
 a link gain setting control loop, coupled between the head end node and the amplifier node, that adjusts a target gain value for the amplifier node. 
 
   
   
     9. The system of  claim 8  wherein the link gain setting control loop adjusts the target gain value in response to a change in a number of the plurality of optical channels. 
   
   
     10. The system of  claim 8 , wherein the amplifier gain control loop is a first amplifier gain control loop, the link gain setting control loop is a first link gain setting control loop, the constant output power is a first constant output power, the target gain is a first target gain value, and the amplifier node is a first amplifier node, the system further comprising:
 a second amplifier gain control loop, coupled across a second amplifier node within the plurality of amplifier nodes, that provides a second constant output power on the second amplifier node across each of the plurality of optical channels; and 
 a second link gain setting control loop, coupled between the head end node and the second amplifier node, that adjusts a second target gain value for the second amplifier node. 
 
   
   
     11. The system of  claim 8  wherein the adjustment to the target gain value is performed by the link gain setting control loop in response to a gain adjust request received by the head end node from the first amplifier node.